It is narrated by ‘Umar bin al-Khattāb that the Prophet (صلى الله عليه وآله وسلم) said:

"Among Allāh’s servants there are some who are neither prophets nor martyrs but on the Day of Judgement the prophets and the martyrs will envy their grades. The Companions asked: ‘O Messenger of Allāh, tell us, who are those people?’ He replied: ‘those are the people who love one another on Allāh’s count. They are neither related to one another nor do they have any property to exchange. I swear on Allāh that they will have faces of light,they will be on pulpits of light. They will not have any fear when others will be afraid, they will not have any grief when others will be aggrieved.’ Then he recited the verse: Beware! No doubt, there is no fear for the friends of Allāh nor shall they be sad and sorrowful. "

[Qur’ān (Yūnus, Jonah) 10:62.]

Abū Dāwūd, Sunan, b. of ijārah (wages) 3:288 (#3527); Bayhaqī, Shu‘ab-ul-īmān, (6:486#8998,8999); Khatīb Tabrīzī, Mishkāt-ul-masābīh, b. of adab (good manners) ch.16 (3:75-6#5012).  [src: Ch3 of Beseeching for Help, Tahir-ul-Qadri]

Allah Most High says: "He who is hostile to a friend of Mine I declare war against. My slave approaches Me with nothing more beloved to Me than what I have made obligatory upon him, and My slave keeps drawing nearer to Me with voluntary works until I love him. And when I love him, I am his hearing with which he hears, his sight with which he sees, his hand with which he seizes, and his foot with which he walks. If he asks me, I will surely give to him, and if he seeks refuge in Me, I will surely protect him"

(Sahih Bukhari - Fath al-Bari, 11.340 41, hadith 6502) [src: suhba.org]